I agree with the previous poster, if you want a cheap binocular avoid roof prisms, they simply cannot be good. Also avoid very small binoculars like 8x20, 10x25 and so on; I had a Nikon 10x21 and it was really usable only in very bright light. So I would go for a 7x35 or 8x30 or 8x40, at least.
I don't know if you wear eyeglasses, but this is a VERY important point. I wear glasses AND I have astigmatism, this means that a binocular without sufficient eye relief for use with glasses is basically useless for me.
I would also recommend the Nikon Action series, they are very good for the price! However if you need to use them with glasses, and want waterproof binoculars, then you should choose the Nikon Action EX, they are still cheap but more expensive that the regular Actions, they are perfect for eyeglass wearers and are waterproof. Moreover they have a metal body which look more robust. Recently I purchased a Nikon Action EX 8x40 as a second binocular, and frankly I was surprised by its quality!
Of course it is not perfect, the outer part of the image is not sharp, and in this it differs from more expensive binos; but the image is very bright, and very sharp in the center, which is mostly important for birdwatching. Moreover it has a very wide FOV, which I find useful. I don't think that for the price you can find anything better.
kmiernik said:
In range of 50$ you just can't get anything with roof prisms with resonable and acceptable quality. Do NOT buy any cheap 8x20 or 10x25 rubbish binoculars unless you won't to throw away 50$. You won't identify or clearly see any bird even in backyard or garden.
I reccomend you Nikon Action VII 7x35. You'll buy them for 60$ and they're something perfect for begginers. Magnification 7x is enough for close range birdwatching and you'll get very bright and clear image due to Porro prisms system. Later on you'll keep them as secondary binoculars to carry them all around.
http://www.opticsplanet.net/nikon-7x35-action.html
One more advice: go somewhere and compare any of those 10x25 with Nikon 7x35.